It is known that vacuum arc cathode plasma is transported and filtered from macroparticles in the crossed electric and magnetic fields, when its electrons are magnetized and ions are un-magnetized. In such conditions, the ions are focused optically, and systems that provide for such focusing are referred to as plasma-optical systems.
Vacuum arc cathode plasma is generated during electric arc evaporation of the cathode material by vacuum-arc cathode spots in the form of high-speed plasma jets and macroparticle flows. Macroparticles are formed from the liquid phase of the vacuum arc cathode spots. Plasma jets can be controlled through magnetic and electric fields. Macroparticles move independently from magnetic or electric fields, virtually on linear paths. They are characterized by a higher mass compared to plasma ions and a small charge per their mass unit. Therefore, macroparticles can be reflected only using appropriate means in the form of screens or captured by special traps. Presence of the means to reflect or capture macroparticles narrow the plasma-guide channel. This causes a significant reduction in the plasma flow at the transport system outlet due to plasma losses in these means.
There is known a method [Reference-1] that provides for transporting of vacuum arc cathode plasma with macroparticle filtering from an electric arc evaporator to a transport system outlet. The transporting is effected in response to a nonlinear time-constant transport magnetic field. The magnetic field is created using electromagnetic coils.
There is known a plasma-optical system [Reference-1] for implementation of the above-described method, which system comprises a plasma guide. The transport magnetic field is established using electromagnetic coils encircling (surrounding) the cathode, the anode, and the plasma guide. In such system, the plasma guide is curved in the shape of a quarter torus and electrically insulated from the anode.
Reduction of plasma transport losses in such curved plasma-optical systems requires powerful magnetic fields or large plasma guide and anode cross-sections. This is a disadvantage of both the above-described method and the device for its implementation. Another disadvantage of the above-described method and system is a significant inhomogeneity of the plasma flow intensity across its section at the plasma guide outlet. A time-averaged plasma flow at the outlet of the plasma source in the above-described plasma-optical system is not uniformly (not evenly) distributed on the deposited surface. Such non-uniform distribution is caused by significant plasma losses during its emission from the peripheral area of the consumable cathode's butt end. Therefore, it is quite a problem to obtain uniform-thickness coatings on the surface with a spot diameter larger than the cathode's diameter without rotating the base about its axis.
The nearest related art (herein called a ‘prototype’) for the claimed method is a method [Reference-2] for transporting of vacuum arc cathode plasma with macroparticle filtering in a plasma-optical system (also described in [Reference-2]) by a transport magnetic field having a constant time component.
The prototype is referred to as a linear plasma-optical system [Reference-2] for transporting vacuum arc cathode plasma. It comprises a cathode; an anode; a plasma guide with electromagnetic coils encircling the cathode and anode; an arc power supply source; and macroparticle reflectors; an electromagnetic deflection coil placed inside an electroconductive tube segment. This tube segment is coaxially placed inside the anode, electrically connected thereto, and is screened on the cathode end.
The electromagnetic deflection coil is designed to create a magnetic field directed opposite to the magnetic field created by the electromagnetic coils encircling the cathode, the anode, and the plasma guide.
When using the aforementioned method and device, plasma flows from the cathode spots of the arc in the vacuum electric arc discharge travel along the transporting magnetic field and travel around the tube segment inside the anode. This somewhat reduces plasma losses due to a reduction of deposits on the section.
However, despite some reduction in such losses, the prototype method, and the prototype system have disadvantages still resulting in significant losses of plasma flows during their transporting. One of such disadvantages is formation of a magnetic mirror in the gap between the inner anode surface and outer lateral surface of the aforesaid tube segment due to increasing the intensity of magnetic field in the longitudinal direction. Thereby, plasma electrons, having kinetic energy in the transverse direction to the magnetic field greater than the one in the longitudinal direction thereto, are captured in a magnetic trap limited by the areas with the magnetic field maxima. One such maximum is located close to the evaporable cathode butt end, while another one is located in the gap between the anode inner surface and outer lateral surface of the aforesaid tube segment. The electrons captured in the magnetic trap, while moving along the magnetic field lines, are repeatedly reflected from magnetic plugs formed in the areas with the magnetic field maxima. These reflections increase their retention time in the area between the magnetic plugs. In this time interval, a significant part of the trapped electrons, proportional to their retention time, escape from the plasma flow to the anode inner surface. Such escape of electrons occurs predominantly due to their drift towards the anode inner surface in response to the electric field cross-polarizing of the plasma jet in the magnetic field. The velocity of such drift is directly proportional to the electric polarization field intensity and inversely proportional to the magnetic field intensity.
The electric polarization field is formed due to magnetized electrons drifting relative to un-magnetized ions across the magnetic field and outer electric field, as well as due to electrons drifting transversely to the magnetic field and its transverse gradient directed towards the outer surface of the aforesaid tube segment. In such conditions, both drifts sum up, thus increasing the plasma jet transverse polarization and, consequently, the velocity of electron drift onto the anode inner surfaces. According to a plasma quasi-neutrality condition, the corresponding number of ions escape the plasma. This respectively reduces the ion current at the anode outlet.
A second disadvantage reducing the average output ion current from a plasma source is caused by the reasons shown below. For a fixed arc current, the difference of potentials between the plasma jet and the anode, or between the plasma jet and the plasma guide, varies consistently due to continuous variations in the positions of arc cathode spots moving across the cathode butt end surface. If the cathode spots move in the peripheral area of the cathode butt end surface, the plasma jets coming out of these spots travel close to the inner surfaces of the screens on the anode and the plasma guide. The closer the plasma jet approaches the anode and plasma guide inner surfaces, the more plasma is lost on these surfaces, thus reducing the ion current from the plasma source. This disadvantage is common for all the existing electric arc plasma sources, wherein transporting the cathode plasma with macroparticle filtering is effected in a similar manner in a similar system, both in the prototype and other related art methods and systems.